Blade arrangement for axial compressors



Aug."ZG, 1946. OLZWEIFEL I 2,406,126 BLADE ARRANGEMENT FOR AXIAL COMPRESSORS- I Filed June 7, 1943 Patented Aug. 20, 1946 arr-Q: P

QOMPRESSQRS' ottb zwiretBaan; Switzerland; d s gn r to Air tien'ge'sellsch'aft Brown, Boveri & Cie., Baden;-

. Switzerland For manufacturing reasons the blading bf multiestage axial type compressors is generally composed ofas many similar stages aspossible'; the majority of the .rows of moving blades as well as most of the ro'wsof stationaryibladesbeing each of the same kind. In the special case o f the so-called; symmetrical. blade arrangement the. moving and stationary blades are. not merely of the .samedesig'n" but the moving and stationary blade are also the image of each other. The entrance and exit angles are also repeated from stage to stage, the only difierence between the stages being the length and twist of the blades. Amongst these blades, which on account of their similarity are designated as normal stages there is a kind where the absolute path of the flow both in front of the stationary blade as well a in front of the moving blades diverges considerably from the axial direction. In order to obtain a smooth entrance into the first stage of such blading it is necessary to give the medium which has to be compressed a certain swirling motion which diverts the flow into the desired circumferential direction.

It is known to produce this entering swirl by giving the entrance spiral of the casing a special with nozzle-like guide elements or by combining both these devices. A disadvantage of all these devices is, however, that the required swirling effeet is only achieved at the expense of a drop in pressure which can only be compensated by additional stages and this means further losses.

The present invention concerns a blade arrangement for axial compressors with a plurality of rows of the same stationaryand the same moving blades or at leastgeometrically similar blades, so-called normal stages, and with a flow of the medium which is to be compressed which diverges considerably from the axial direction both in front and after each guide row, so that the medium which is to be compressed in order to achieve a smooth entry must receive a certain swirl, this swirl being mainly produced by a moving blade row which is located in front of the I first moving blade row of the normal stage blading. The normal construction of blading according to one form of the invention thu commences with two rows of moving blades the second of which is a moving blade row of a normal stage.

The invention is explained by means of three constructional examples shown in the accompanying drawing the first of which, Figs. 1 to 4, refers to the hitherto known arrangement of blading, whilst the second example illustrated in can; (or. 230-122) form or by means of a row of stationary blades 7 Figs? 5 m1 8 deals with thenovell corrstructio' cordinto' the invention andFig. 9 shows a special'modified form qi' tne invention.

The axial blower shown diagrammatically in secti n in Fig-.- -1 comprises fivesyrnmetricalnor- .mal stages which' each include" mew of rotating? blades sand a row of stationary "blades -3i The swirl wnienmust e'ii paneq tofthenow n rd r to obtainiin" accordance withthe direc 1on of-flow 02 (Fig? 4) a siiiootri enn lhbi J llE fiI St moving blade row (Fig. 2) is achieved by the stationary blade row I. This blade row consists of heavily curved guide blades in which the medium has its axial velocity or changed to a velocity 02. Corresponding to the increase in velocity there is a decrease in pressure (Fig. 3) which can onlybe compensated again in the subsequent compressor stages.

With the arrangement according to the inven- 7 tion the guide row I in Fig. 1 is replaced by a specially shaped moving blade row 4 as shown in Figs. 5' and 6. The relative velocity wi (Fig. 8)

corresponding to the absolute axial velocity 01 is respects. The circumferential components of the relative velocities of the additional moving blade row are considerably higher than those of the 7 moving blade row of the normal stages and the entrance angles are therefore acuter.

The blade does, however, not need to be bigger.

Although the usual form of the invention is with two independent. rows of moving blades it is also possible to combine both rows to form a single row. The profile of these combined moving blades is then composed of a blade part which at the inlet possesses the angleand profile conditions of the guide blades in the supplementary moving rowand of a trailing blade part which has the same angle and profile conditions as a moving compressor blade of the normal stages.

This combined construction is shown in Fig. 9.

In the blade 5 which is a combination of the blades 2 and 4 the velocity w of Fig. 8 must bedirectly reduced to wa. The advantage of this combination is that a row of blades can be dispensed with.

. I 3 Slightly higher flow losses due to the greater deviation have, however, to be taken into account. Since the first row of moving blades of the normal stages is combined with the supplementary row in front of the normal stages the first moving row is "immediately followed bya normalstationary row3. Under certain conditions it i also possible to use the same profiles for the supplementary movg ing blades as for the moving rows of the 'normal stages. The blades of the supplementary; row '-must, however, be 50 arranged that their angle to the circumferential direction i considerablyceeding normal stages.

In addition to the moving bladerow the shape of the inlet casing can also assist'in impartL'a swirling effect on the medium.

I claim:

1. In an axial flow gascompressor, the com- 20 bination with v a; plurality pi -compressor; stages comprising alternately-arranged rows of rotating and of stationary blade of geometrically similar profile, of a first compressor stage preceding said plurality of compressor stages; said first compres rsia n 's r w o ab narygb ades f h s m profile thelrqws o st t ona bla es iffse p ura diecm es rl t s s, n ro ate ing blade means preceding said row of stationary blade 'forf-imparting a circumferential compo 3n more acute than the entrance angle "of the sue-e} prOfileas the rotating blades nent to the gas as it enters said first compressor" stage and for discharging the gas therefrom at substantially the same angle as that at which gas is discharged from the rotating blades of each of said plurality of compressor stages, said rotating blade means having an entrance angle more acute with respect to the axial direction of gas flow than the corresponding entrance angle of the rotating blades' of said plurality of compressor stages and having a discharge angle identical with the corresponding discharge angle of the rotatin "blades of said plurality of compressor stages.

2. In an axial flow gas compressor, the invention as recitedin claim 1, wherein said rotating blade means comprisesan inlet row of blades having said more acute entrance angle, and a second .row of blades between said inlet row and said row of stationaryblades of the first compressor stage,

" said second row of blades having the same profile as the rotating blades of said plurality of compressor stages. Q 3 ..V

"3. In an axial flow gas compressor, the invention as recited :in claim 1, wherein said rotating blade means comprisesa single row of blades having entrance'portions of saidmore'acute entrance angle and trailing portions of the same angleand of said plurality-of compressor stages. i l

- 7 OTTO'ZWEIFEL; 

